This application claims priority to European Application Serial Number 00 870 149.2, filed Jun. 30, 2000, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a damping device of xe2x80x9csqueeze filmxe2x80x9d type which acts as a pressurized-oil damper, integrated in a rolling bearing, which is intended in particular to be used in civil aeronautics.
Specifically, the invention relates to the rolling bearing using the damping device.
2. Description of Related Art
A rolling bearing such as, for example, in an aircraft engine, serves as a link between one or more inner mobile members, preferably having a revolution symmetry and rotating about an axis, and an outer structural component. The outer structural component may itself be either fixed or mobile. This structure also has a revolution symmetry relative to the rotational axis of the mobile member(s). It may be, for example, in the shape of a cone.
The rolling bearing consists substantially of balls or rollers which move on tracks that are securely fastened or made with races, preferably an inner race and an outer race.
When working, forces are transmitted from the mobile member to the outer structural component, in particular via the outer rolling race, which is directly in contact with the outer structural component.
In order to damp the effect of these forces, it is known to confine a film of oil between the outer rolling race, which works by friction, and the outer structural component. This film of oil is commonly known as a xe2x80x9csqueeze filmxe2x80x9d.
The oil present at the race/outer structural component contact surface is oil under pressure, which acts as a damper.
Most of the known xe2x80x9csqueeze filmsxe2x80x9d annulus are made leakproof by means of seals in the form of segments of xe2x80x9cpistonxe2x80x9d type. These seals are placed in two annular grooves machined in the race at its surface of contact with the outer structural component. The film of oil is consequently more particularly confined in the space delimited by these two annular grooves.
When the bearing is located at the extremity of the rotation shaft and submitted to an axial force, it is referred to as a thrust bearing. In this particular case, an additional problem comes from the fact that this type of bearing has to be provided with a centring system which has to take over this axial force. This is particularly important at full working speed.
Therefore, it has been proposed, according to the state of the art, to use a metallic cage consisting in bolted rods as joining members between the outer race, at one of their extremities, and the external structure, which is usually fixed, at the other extremity of the bolted rods.
The main problem is therefore double: it lies in the leaktightness of such a classical device and in the centring of said device relatively to the axial force.
Document U.S. Pat. No. 4,175,803, in particular, describes the xe2x80x9csqueeze filmxe2x80x9d technique constituting a pressurized-oil damper, used particularly in engines of gas turbine type.
In these engines, two rolling bearings are used to maintain in a fixed structure, at its ends, the shaft bearing the vanes of the compressor and of the low-pressure turbine.
Similarly, two other rolling bearings are used to maintain in rotation, about the abovementioned shaft, the shaft bearing the vanes of the compressor and the vanes of the high-pressure turbine. One of the bearings bears on the abovementioned shaft, and the other bears on the fixed structure.
These four rolling bearings are examples of the field of application of the present invention.
The bearings are subjected to vibrations brought about by certain imbalances. During these vibrations, the hydraulic damping film (known as the xe2x80x9csqueeze filmxe2x80x9d) is xe2x80x9ccrushedxe2x80x9d at a point of the annular space which exists between the outer race and the outer structural component surrounding this race.
The vibrations drive this xe2x80x9ccrush pointxe2x80x9d in an orbital (precessional) motion along the annular space.
The presence of oil maintained under pressure in the annular space, by means of the orbital motion, has the effect of creating a damping of the vibration.
In order to produce a sufficient and stable damping, it is desirable to maintain the xe2x80x9csqueeze filmxe2x80x9d annulus by means of a sealing device.
Most of the xe2x80x9csqueeze filmsxe2x80x9d proposed comprise seals of the same type as the piston segments of motor vehicle engines and they act at least partially by a radial pressure, such as, for example, in document FR-A-2,517,772.
This type of seal has various drawbacks. Dynamic seals of piston-segment type must be machined with great precision. They are thus expensive. Furthermore, they are intricate to mount. Finally, they have an uncalibrated oil leakage and thus their damping is not always fully controlled.
Furthermore, this arrangement requires a certain space for installing the oil damper, especially for installing the centring rods about the motor axis. Therefore, this arrangement remains inappropriate for small turning devices. In addition, the assembling of this type of structure is relatively complex.
Document U.S. Pat. No. 3,756,672 discloses a pressurized oil damper, wherein the race is in contact with two side seals. However, these seals are not directly attached to said race. A rotational movement of said race relative to the bearing is thus made possible.
Documents U.S. Pat. No. 5,251,985, U.S. Pat. No. 4,337,983, U.S. Pat. No. 3,652,139 and U.S. Pat. No. 5,058,452 describe various embodiments, wherein seals are directly in contact with the outer race by clamping. Again, in these different cases, the seals may rotate relatively to said race.
The fact that seals may still rotate relatively to said race will further reduce the leaktightness of the device.
The present invention aims to provide a solution that ensures a good leaktightness of the oil film constituting the xe2x80x9csqueeze filmxe2x80x9d damper of a bearing.
The present invention aims to provide a solution which prevents any free rotation of the seals, especially at the base, but which still allows said seals to achieve a precessional motion relative to it.
The present invention further aims to ensure, in the particular case of a thrust bearing, the axial retention of the outer race relative to the outer structural component.
The present invention aims also to propose an alternative solution, wherein no space for installing centring rods is required, and for which the assembling of the various pieces is easy to perform.
Other aims and advantages will come to light through the reading of the following description.
Main Characteristic Elements of the Invention
The present invention is related to a bearing for maintaining an inner mobile structural component having a revolution symmetry, rotating inside an outer structural component, which is itself fixed or mobile, said bearing comprising a set of balls or rollers and at least an outer rolling race which provides the mechanical contact between said balls or rollers and said outer structural component, said bearing also comprising a pressurized-oil damper known as a xe2x80x9csqueeze filmxe2x80x9d damper, arranged at the annular contact surface between said outer race and the outer structural component, characterized in that each side surface of the outer race is in contact with a side seal having an annular form, said seals being securely fastened to the outer race by means of a series of anti-rotation fixing members.
The side seals may be made at least partially of carbon.
Preferably, the side faces of each seal are coated at least partially with a coating comprising carbon.
Advantageously, the side seals are submitted to a precompression stress.
According to a first preferred embodiment, said precompression stress is achieved by gripping said outer race by means of Smalley springs.
According to a second preferred embodiment, said precompression stress is achieved by gripping said outer race by means of Belleville washers.
The present invention is also related to the use of the bearing disclosed hereabove as a thrust bearing arranged at the end of a rotating shaft.